Index: share/man/man4/smp.4
===================================================================
--- share/man/man4/smp.4
+++ share/man/man4/smp.4
@@ -23,7 +23,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd January 6, 2018
+.Dd December 22, 2018
 .Dt SMP 4
 .Os
 .Sh NAME
@@ -35,27 +35,6 @@
 The
 .Nm
 kernel implements symmetric multi-processor support.
-.Sh COMPATIBILITY
-Support for multi-processor systems is present for all Tier-1
-architectures on
-.Fx .
-Currently, this includes amd64, i386 and sparc64.
-Support is enabled using
-.Cd options SMP .
-It is permissible to use the SMP kernel configuration on non-SMP equipped
-motherboards.
-.Sh I386 NOTES
-For i386 systems, the
-.Nm
-kernel supports motherboards that follow the Intel MP specification,
-version 1.4.
-In addition to
-.Cd options SMP ,
-i386 also requires
-.Cd device apic .
-The
-.Xr mptable 1
-command may be used to view the status of multi-processor support.
 .Pp
 .Nm
 support can be disabled by setting the loader tunable
@@ -66,6 +45,13 @@
 the read-only sysctl variable
 .Va hw.ncpu .
 .Pp
+The number of online threads per CPU core is available in the read-only sysctl
+variable
+.Va kern.smp.threads_per_core .
+The number of physical CPU cores detected by the system is available in the
+read-only sysctl variable
+.Va kern.smp.cores .
+.Pp
 .Fx
 allows specific CPUs on a multi-processor system to be disabled.
 This can be done using the
@@ -74,6 +60,12 @@
 Setting this tunable to 1 will result in the corresponding CPU being
 disabled.
 .Pp
+.Fx
+supports simultaneous multithreading on x86 and powerpc platforms.
+On x86, the logical CPUs can be disabled by setting the
+.Va machdep.hyperthreading_allowed
+tunable to zero.
+.Pp
 The
 .Xr sched_ule 4
 scheduler implements CPU topology detection and adjusts the scheduling
@@ -122,13 +114,26 @@
 .Pp
 This information is used internally by the kernel to schedule related
 tasks on CPUs that are closely grouped together.
-.Pp
-.Fx
-supports hyperthreading on Intel CPU's on the i386 and AMD64 platforms.
-Because using logical CPUs can cause performance penalties under certain loads,
-the logical CPUs can be disabled by setting the
-.Va machdep.hyperthreading_allowed
-tunable to zero.
+.Sh COMPATIBILITY
+Support for multi-processor systems is present for all Tier-1 and Tier-2
+architectures on
+.Fx .
+Currently, this includes x86, powerpc, arm, and sparc64.
+Support is enabled using
+.Cd options SMP .
+It is permissible to use the SMP kernel configuration on non-SMP hardware.
+.Sh I386 NOTES
+For i386 systems, the
+.Nm
+kernel supports motherboards that follow the Intel MP specification,
+version 1.4.
+In addition to
+.Cd options SMP ,
+i386 also requires
+.Cd device apic .
+The
+.Xr mptable 1
+command may be used to view the status of multi-processor support.
 .Sh SEE ALSO
 .Xr cpuset 1 ,
 .Xr mptable 1 ,
@@ -166,3 +171,20 @@
 also introduced support for SMP on the sparc64 architecture.
 .Sh AUTHORS
 .An Steve Passe Aq Mt fsmp@FreeBSD.org
+.Sh CAVEATS
+The
+.Va kern.smp.threads_per_core
+and
+.Va kern.smp.cores
+sysctl variables are provided as a best-effort guess.
+If an architecture or platform adds SMT and
+.Fx
+has not yet implemented detection, the reported values may be inaccurate.
+In this case,
+.Va kern.smp.threads_per_core
+will report
+.Dv 1
+and
+.Va kern.smp.cores
+will report the same value as
+.Va hw.ncpu .
Index: sys/kern/subr_smp.c
===================================================================
--- sys/kern/subr_smp.c
+++ sys/kern/subr_smp.c
@@ -101,6 +101,14 @@
 SYSCTL_INT(_kern_smp, OID_AUTO, cpus, CTLFLAG_RD|CTLFLAG_CAPRD, &smp_cpus, 0,
     "Number of CPUs online");
 
+int smp_threads_per_core = 1;	/* how many SMT threads are running per core */
+SYSCTL_INT(_kern_smp, OID_AUTO, threads_per_core, CTLFLAG_RD|CTLFLAG_CAPRD,
+    &smp_threads_per_core, 0, "Number of SMT threads online per core");
+
+int mp_ncores = -1;	/* how many physical cores running */
+SYSCTL_INT(_kern_smp, OID_AUTO, cores, CTLFLAG_RD|CTLFLAG_CAPRD, &mp_ncores, 0,
+    "Number of CPUs online");
+
 int smp_topology = 0;	/* Which topology we're using. */
 SYSCTL_INT(_kern_smp, OID_AUTO, topology, CTLFLAG_RDTUN, &smp_topology, 0,
     "Topology override setting; 0 is default provided by hardware.");
@@ -157,6 +165,7 @@
 
 	/* Probe for MP hardware. */
 	if (smp_disabled != 0 || cpu_mp_probe() == 0) {
+		mp_ncores = 1;
 		mp_ncpus = 1;
 		CPU_SETOF(PCPU_GET(cpuid), &all_cpus);
 		return;
@@ -165,6 +174,11 @@
 	cpu_mp_start();
 	printf("FreeBSD/SMP: Multiprocessor System Detected: %d CPUs\n",
 	    mp_ncpus);
+
+	/* Provide a default for most architectures that don't have SMT/HTT. */
+	if (mp_ncores < 0)
+		mp_ncores = mp_ncpus;
+
 	cpu_mp_announce();
 }
 SYSINIT(cpu_mp, SI_SUB_CPU, SI_ORDER_THIRD, mp_start, NULL);
@@ -826,6 +840,7 @@
 mp_setvariables_for_up(void *dummy)
 {
 	mp_ncpus = 1;
+	mp_ncores = 1;
 	mp_maxid = PCPU_GET(cpuid);
 	CPU_SETOF(mp_maxid, &all_cpus);
 	KASSERT(PCPU_GET(cpuid) == 0, ("UP must have a CPU ID of zero"));
Index: sys/powerpc/powernv/platform_powernv.c
===================================================================
--- sys/powerpc/powernv/platform_powernv.c
+++ sys/powerpc/powernv/platform_powernv.c
@@ -435,6 +435,8 @@
 		break;
 	}
 
+	smp_threads_per_core = nthreads;
+
 	if (mp_ncpus % nthreads != 0) {
 		printf("WARNING: Irregular SMP topology. Performance may be "
 		     "suboptimal (%d threads, %d on first core)\n",
@@ -442,6 +444,8 @@
 		return (smp_topo_none());
 	}
 
+	mp_ncores = mp_ncpus / nthreads;
+
 	/* Don't do anything fancier for non-threaded SMP */
 	if (nthreads == 1)
 		return (smp_topo_none());
Index: sys/powerpc/powerpc/mp_machdep.c
===================================================================
--- sys/powerpc/powerpc/mp_machdep.c
+++ sys/powerpc/powerpc/mp_machdep.c
@@ -186,6 +186,11 @@
 next:
 		error = platform_smp_next_cpu(&cpu);
 	}
+
+#ifdef SMP
+	/* Probe mp_ncores and smp_threads_per_core as a side effect. */
+	(void)cpu_topo();
+#endif
 }
 
 void
Index: sys/powerpc/ps3/platform_ps3.c
===================================================================
--- sys/powerpc/ps3/platform_ps3.c
+++ sys/powerpc/ps3/platform_ps3.c
@@ -246,6 +246,8 @@
 static struct cpu_group *
 ps3_smp_topo(platform_t plat)
 {
+	mp_ncores = 1;
+	smp_threads_per_core = 2;
 	return (smp_topo_1level(CG_SHARE_L1, 2, CG_FLAG_SMT));
 }
 #endif
Index: sys/powerpc/pseries/platform_chrp.c
===================================================================
--- sys/powerpc/pseries/platform_chrp.c
+++ sys/powerpc/pseries/platform_chrp.c
@@ -517,6 +517,8 @@
 		ncpus++;
 	}
 
+	mp_ncores = ncores;
+
 	if (ncpus % ncores != 0) {
 		printf("WARNING: Irregular SMP topology. Performance may be "
 		     "suboptimal (%d CPUS, %d cores)\n", ncpus, ncores);
@@ -527,6 +529,7 @@
 	if (ncpus == ncores)
 		return (smp_topo_none());
 
+	smp_threads_per_core = ncpus / ncores;
 	return (smp_topo_1level(CG_SHARE_L1, ncpus / ncores, CG_FLAG_SMT));
 }
 #endif
Index: sys/sys/smp.h
===================================================================
--- sys/sys/smp.h
+++ sys/sys/smp.h
@@ -174,8 +174,10 @@
 
 extern u_int mp_maxid;
 extern int mp_maxcpus;
+extern int mp_ncores;
 extern int mp_ncpus;
 extern volatile int smp_started;
+extern int smp_threads_per_core;
 
 extern cpuset_t all_cpus;
 extern cpuset_t cpuset_domain[MAXMEMDOM]; 	/* CPUs in each NUMA domain. */
Index: sys/x86/x86/mp_x86.c
===================================================================
--- sys/x86/x86/mp_x86.c
+++ sys/x86/x86/mp_x86.c
@@ -604,6 +604,7 @@
 {
 	struct topo_node *node;
 	u_int smt_mask;
+	int nhyper;
 
 	smt_mask = (1u << core_id_shift) - 1;
 
@@ -612,6 +613,7 @@
 	 * beyond MAXCPU.  CPU 0 is always assigned to the BSP.
 	 */
 	mp_ncpus = 0;
+	nhyper = 0;
 	TOPO_FOREACH(node, &topo_root) {
 		if (node->type != TOPO_TYPE_PU)
 			continue;
@@ -639,6 +641,9 @@
 			continue;
 		}
 
+		if (cpu_info[node->hwid].cpu_hyperthread)
+			nhyper++;
+
 		cpu_apic_ids[mp_ncpus] = node->hwid;
 		apic_cpuids[node->hwid] = mp_ncpus;
 		topo_set_pu_id(node, mp_ncpus);
@@ -648,6 +653,9 @@
 	KASSERT(mp_maxid >= mp_ncpus - 1,
 	    ("%s: counters out of sync: max %d, count %d", __func__, mp_maxid,
 	    mp_ncpus));
+
+	mp_ncores = mp_ncpus - nhyper;
+	smp_threads_per_core = mp_ncpus / mp_ncores;
 }
 
 /*